1. Field of the Invention
This invention relates generally to the field of air quality and more particularly to an apparatus and method for purifying air.
2. Description of Related Art
Air purifiers generally consist of filter units driven by fans. The filters may be particulate filters followed by activated charcoal or other filter types. In general, the fans are noisy, and the filters need often replacement.
Some devices have been built using photocatalysts activated by ultraviolet light. In general these have been wall panels, or filter devices again driven by fans. U.S. Pat. No. 5,919,422 teaches a number of configurations where ambient air in a container simply reacts with the photocatalyst by diffusion. This method will work for a small container, but needs the addition of a fan to purify air in an entire room. U.S. Pat. No. 5,945,372 teaches a photocatalyst used in building HVAC systems (with large fans) to purify air in buildings.
What is badly needed is a small device that can be directly plugged into a wall electrical socket that contains no moving or replaceable parts. This device should, over a period of hours, purify the air in a room by killing bacteria, removing organic compounds, and possibly even converting poisons such as carbon monoxide into something more harmless such as carbon dioxide. The device must be quiet, since it would be left in a room both day and night. Its purifying element must never need replacement. It must not produce too much heat, and it should not need any maintenance.
The present invention relates to an apparatus and method for purifying air in a room. The invention causes air to pass through a vertical passageway or chimney (reactor) that contains a photocatalyst that is activated by an ultraviolet light source. Air is caused to move by a process called natural convection whereby no external force such as a fan needs to be used. Natural convection occurs when air is heated by a hot body and hence becomes less dense than colder surrounding air. The less dense air experiences an increase in upward buoyancy force which causes it to move upward. The present invention can contain a small heater or heat element in a vertical passageway or chimney (reactor). Cold air can enter the apparatus through slots or openings at the bottom of the device. An optional filter can be placed here to remove particulate matter. A heater or heat element can be placed above the air entrance port or filter if a filter is present. This heater causes natural convection to take place. As the warmer air moves upward, a pressure gradient is formed which in turn draws more cool air into the device.
The slightly heated air passes up through the chimney or reactor passageway where it encounters a photocatalyst such as titanium dioxide either in pure form or doped with any of several metals. The photocatalyst is activated by an ultraviolet light source that emits light with a wavelength or spectrum shorter than 387 nanometers (which is the activation energy of pure titanium dioxide in the anatase crystal form), or shorter than the activation energy of whatever catalyst is used.
The photocatalyst is held in the chimney in a form which exhibits a large surface area to allow maximum exposure of the air that is convecting upward. The photocatalyst can be coated on a flat sheet which in turn can be spiraled on a loose spool to obtain more surface area of exposure, or the photocatalyst can be impregnated on fibers which can be formed into a fibrous mass (an example of such fibrous mass might be fiberglass insulation or a like fiber). The fibers can be natural or synthetic organic materials, or can be glass such as fiberglass. Any means of holding the photocatalyst in position so that air passing upward in the chimney makes contact with it is within the scope of the present invention.
The ultraviolet light source that is used to activate the photocatalyst can be a commercial UV light bulb, a fluorescent lamp (which leaks considerable UV light), or a means of allowing sunlight to enter the device. If a UV bulb is used, an optional power supply usually must be used to supply the bulb voltage.
The present invention contains an exit port on its top which can be slots or a small jet to allow the upward convecting air to re-enter the room. This port can contain an optional baffle to prevent UV light from entering an observer""s eyes. This type of protection is necessary if wavelengths shorter than about 340 nanometers are used. It may also be desirable in some cases to prevent any visible light produced by the UV source from exiting the device. In other cases, it may desirable to allow visible light to exit the device so that the present invention can also be used as a night light while it purifies the air.
The present invention can be equipped with two electrical prongs on its back side so that it can be directly plugged into a standard 110 V. electrical outlet, or, optionally, it can have a power cord. Power from the electrical outlet can be used to supply energy to both the heater and to the ultraviolet light source. The direct electrical connection is optional since the present invention can also be run directly from batteries.
The present invention purifies air in a room over a span of hours since the rate of natural convection is slow. The invention can kill bacteria and can convert organic compounds such as volatile organics (VOC""s), odor causing organics, hydrocarbons, and other undesirable compounds into smaller, less harmful or odorous, compounds such as carbon dioxide, water.